This invention relates to a control mechanism for a realistic robot constructed on modelling the mechanism or the operation of a living body. More particularly, the present invention relates to a control mechanism for a legged mobile robot which has modelled the bodily mechanism of an animal movable on legs, such as human being or monkeys.
More specifically, the present invention relates to a circuit mechanism for a legged mobile robot that can be widely applied in a living space and living environment of the human being and, more specifically, to the control method mechanism of a legged mobile robot that is able to adaptively control its attitude to continue its operation without falling.
The mechanism exploiting the electrical or magnetic action to execute a motion resembling the operation of the human being is called a robot. The word robot is said to originate from ROBOTA (slave machine). The robot came into widespread use towards the end of the sixties. The majority of the robots were industrial robots, such as manipulators or transporting robots, aimed at realization of automation or unmanned production operations in plants.
Recently, researches and development in legged mobile robots, simulating the body mechanism or operations of an animal walking in upstanding attitude on two legs, such as human being or robots, have made rapid progress such that practical utilization thereof is felt to be promising. Although motion on two legs is unstable and present difficulties in attitude or walking control as compared to that on four or six legs, it is excellent in realization of flexible motion operations, such as accommodation to walking surfaces presenting irregularities on the working path, such as non-bulldozed lands or lands presenting obstacles, or to non-continuous walking surfaces, such as staircases or ladders.
The legged mobile robots, emulating the mechanism of a human being, are called xe2x80x9chuman typexe2x80x9d or xe2x80x9chuman stylexe2x80x9d robots (humanoid robots). The humanoid robot is able to perform life support for the human being, that is to support human activities in our living environments or our everyday life.
The significance of making researches and development in a robot called a humanoid robot can possibly be grasped from the following two viewpoints.
One of them is that from the human science. That is, through the process of creating a robot having a structure resembling a leg and/or a foot of a human being, devising its control method and simulating the walking performance of the human being, it is possible to technically elucidate the mechanism of the natural human behavior such as walking as the first and foremost human behavior. The results of these researches will appreciably contribute to significant progress in a variety of research fields handling human motion mechanisms in the human engineering, rehabilitation engineering and in the sports sciences.
The other is development of a robot supporting our lives as human partners, that is supporting human activities in various situations in our living environments and in our everyday lives. This sort of the robot needs to learn how to adapt itself to human beings with different personalities or to different environments to make further growths in functional aspects as it learns the performance or manners from the human being in various aspects of our living environments. It may be contemplated that, if the robot is the humanoid robot, that is if the robot is of the same shape or structure as the human being, the robot will operate effectively in having smooth communication with the human being.
For example, if it is necessary to teach a robot to pass through a room as it evades an obstacle it is not allowed to tramp, the user (operator) must find it easier to teach the robot, while the robot will find it easier to learn, if the robot is able to walk on two legs like the human being, than if the robot is of the crawler type or of the four-legged type (see, for example, Takanishi, xe2x80x9cControl of a Robot Walking on Two Legsxe2x80x9d), appearing in xe2x80x9cKo-Soxe2x80x9d, Car Technique Society, Kanto Branch, No.25, 1996 April).
The majority of the human working or living spaces are realized to suit to the bodily mechanism or behavioral pattern of the human being in the form of upstanding walking on two legs. Stated differently, a large number of obstacles are present in the human living space for the present-day mechanical system having wheeled or the like driving devices as motion means. So, in order for the robot as a mechanical system to operate on behalf of the human being in a variety of human operations and to adapt itself more intricately to the living space of the human being, it is desirable that the range of possible motion of the robot be approximately equal to that of the human being. This accounts for expectations generally entertained in the realization of legged movable robots. The fact that the robot has a human type style may be said to be indispensable in elevating the affinity to the human living environment.
Among the usages of the human type robot, there is the usage of taking over the miscellaneous operations in the industrial and productive activities. Examples of these are maintenance operations in nuclear power plants or thermal power plants, transport and/or assembling operations of component parts in petrochemical plants, maintenance operations in high-rise buildings and rescue operations in conflagration or the like calamities.
Among other usages of the human type robots, there is a usage of life adherent type usage, that is the usage aimed at co-existence with human being, rather than life supporting type usage, such as taking over difficult or painful operations. It is a supreme object of this type of robot to faithfully reproduce the full body exercising type operating mechanism proper to an animal walking on two legs, such as human being or monkeys. Moreover, the human type robot, emulating the animal of high intellect, such as human being or monkeys, is desirably spontaneous in its performance exploiting its four limbs as a living body besides being expressive in its behavior. In addition, the human type robot is required not only to execute the pre-input operating pattern faithfully, but also to realize vivid behavioral expressions responsive to the words or demeanor of the human being such as praising or admonition. In this meaning, the entertainment-oriented human type robot, emulating the human being, may be worth being called a xe2x80x9chuman typexe2x80x9d robot.
In a well-known manner, the human being has hundreds of articulations, that is hundreds of degrees of freedom. Although it is desirable to afford approximately the same number of degrees of freedom to the legged movable robot in order to impart the performance as close to that of the human being as possible, this is technically of utmost difficulty. The reason is that, although at least one actuator needs to be provided for each degree of freedom, it is well-nigh impossible to have hundreds of actuators mounted on a robot as a mechanical device because of designing limitations in weight or size. On the other hand, if there are many degrees of freedom, the volume of calculations for robot positions, behavioral pattern control or attitude stabilization control, is exponentially increased.
From this reason, the routine practice is to construct the human type robot with the degrees of freedom on the order of tens of articulations which is appreciably smaller than those of the human beings. Therefore, in designing and control of the human type robot, it may be said to be crucial how more spontaneous performance is to be realized with the smaller number of degrees of freedom.
The legged mobile robot walking on legs is superior in being able to walk or run flexibly such as walking or running on a staircase or over an obstacle, however, it is difficult to control in attitude or stable walking because the number of legs is smaller and the center of gravity position is elevated. In particular, in the case of a humanoid robot, it is necessary to control the body attitude or stabilized walking as the spontaneous motion or feeling of an intellectual animal such as a human being or a monkey is expressed plentifully.
A large number of proposals have already been made in the technology pertinent to attitude control or stable walking in the legged mobile robot walking on two legs. The stable xe2x80x9cwalkingxe2x80x9d herein may be defined to mean xe2x80x9cMotion using legs without falling downxe2x80x9d.
For evading robot falling, stable attitude control of the legged mobile robot is of utmost importance, because falling means interruption of the operation being executed by the robot and a lot of loss in time and labor for the robot to erect itself from its fallen state to re-initiate the operation, and also because the falling tends to inflict fatal damage not only to the robot itself but also to the object colliding against the robot. Therefore, stable attitude control and prevention of falling during walking may also be said to be of utmost importance in the designing and engineering of the legged mobile robot.
During walking, the force of gravity and inertia as well as the moments thereof act from the walking system to the road surface due to the force of gravity and the acceleration generated by the walking motion. The so-called d""Alembert""s principle states that these are counterbalanced by the reactive force from the floor as the reaction from the road surface to the walking system, and the moments thereof. As the conclusion of the mechanical deduction, there is present a point of zero pitching and rolling moments, that is the zero moment point xe2x80x9cZMPxe2x80x9d on one of the sides of a supporting polygon constituted by the road surface and contact points of the foot soles with the floor, or on the inner sides thereof.
The majority of the proposals in stable attitude control and prohibition of falling during walking use this ZMP as the criterion of verifying the walking stability. The two-legged walking pattern generation based on the ZMP criterion has many advantages, such as pre-settable foot sole contact point with the floor surface or ease in taking account of the local constraint conditions of the leg tip conforming to the road surface shape.
For example, the Japanese Laying-Open Patent H-5-305579 discloses a walking control device for a legged mobile robot, in which the ZMP (zero moment point), that is a point on the floor surface where the moment by the reactive force from the floor during walking is equal to zero, is controlled to be coincident with a target value.
The Japanese Laying-Open Patent H-5-305581 discloses a legged mobile robot in which the ZMP is designed to be within the inside of a supporting polygon or at a position of certain allowance from the end thereof when the leg of the robot touches or leaves the floor surface. The result is certain ZMP allowance by a pre-set distance even under disturbances thus contributing to improvement in walking stability.
Moreover, the Japanese Laying-Open Patent H-5-305583 discloses controlling the walking speed of the legged mobile robot depending on the target ZMP position. That is, the legged mobile robot disclosed in the above-referenced publication uses pre-set walking pattern data and is adapted for driving the leg joints to bring the ZMP into coincidence with the target position while detecting the tilt of the upper limb portion to change the walking pattern data emitting speed pre-set depending on the detected value. As a result, if the robot is tilted forwards as it tramps on unexpected irregularities, the emitting speed may be increased to recover its attitude. Also, since the ZMP can be controlled to its target position, the emitting speed can be changed without any impediments when both legs of the robot touch the floor surface.
The Japanese Laying-Open Patent H-5-305585 discloses controlling the floor surface touching position of the legged mobile robot by the ZMP target position. That is, the legged mobile robot disclosed in this publication detects an error between the ZMP target position and the measured position and drives one or both legs in a direction to cancel out the error. Alternatively, the legged mobile robot detects the moment about the ZMP target position and drives the leg to reduce the moment to zero to realize stable walking.
On the other hand, the Japanese Laying-Open Patent H-5-305586 discloses controlling the inclined position of the legged mobile robot by the ZMP target position. That is, the legged mobile robot disclosed in this publication detects the moment about the ZMP target position and, in the presence of a moment, the legs are controlled to reduce the moment to zero to realize stable walking.
The external force to which the legged mobile robot is subjected during walking performance is the reactive force from the floor as the reaction from the floor surface to the walking system. So, by searching the ZMP corresponding to zero pitching and rolling moments on or inside of the sides of the supporting polygon constituted by the foot sole touching point on the floor and the floor surface, it is possible to realize a stable walking performance. The above-mentioned conventional techniques perform adaptive control to the reactive force from the floor.
However, since the legged mobile robot supports or takes over a variety of human operations in the same living space or environment as that of the human being, and ultimately is aimed at co-existence with the human being, the operations actually executed by the legged mobile robot are not simply limited to the walking performance.
The natural consequence of this is that the external force to which the legged mobile robot is subjected in the human living space or environment is not limited to the reactive force from the floor surface.
For example, an entertainment-oriented humanoid robot may take part as a player in a ball game, such as soccer game. In such case, an external force may be applied to the leg or head during kicking or heading of a soccer ball. Moreover, in a karate game, considerable external force tends to be applied to the robot when applying or evading a foot trick.
For example, when a soccer ball, for example, is to be kicked at an elevated speed, a strong reactive force is applied from the soccer ball, as a result of which the robot tends to be unstable or even fallen. If the robot is fallen, not only is the operation discontinued, but the robot tends to be fatally damaged under an impact on falling. In addition, on falling, the counterpart side person or robot tends to be injured or destroyed.
Thus, for realizing extensive application of the legged mobile robot to the human living space or environment, it is necessary, realize to make adaptive control of the legged mobile robot under assumption of a variety of types of external forces.
It is therefore an object of the present invention to provide an control mechanism for the legged mobile robot extensively applicable in the human living space or environment.
It is another object of the present invention to provide a control method mechanism for a legged mobile robot in which it is possible to effect adaptive position control against a variety of external forces to continue the operation without the risk of falling.
In a first aspect, the present invention provides an apparatus for adaptively controlling motions of a legged mobile robot, made up at least of lower limbs, a body trunk and a waist part, against an external force, in which the apparatus includes first setting means for setting leg motion, body trunk motion and upper limb motion, and the attitude and height of the waist part, for realizing the required motion, second setting means for setting a ZMP trajectory based on the leg motion as set by the first setting means, third setting means for setting an external force pattern applied to the legged mobile robot, calculating means for calculating the moment generated on a ZMP as set by the second setting means based on the leg motion, body trunk motion, upper limb motion and the attitude and height of the waist part as set, means for finding a solution of the waist motion for which the moments as calculated by the calculating means are in equilibrium and means for executing the full body exercise motion based on the solution of the waist motion. The present invention also providers a corresponding control method.
In a second aspect, the present invention provides an apparatus for adaptively controlling motions of a legged mobile robot, made up at least of lower limbs, a body trunk and a waist part, against an external force, in which the apparatus includes first setting means for setting leg motion, body trunk motion and upper limb motion, and the attitude and height of the waist part, for realizing the required motion, second setting means for setting a ZMP trajectory based on the leg motion as set by the first setting means, third setting means for setting an external force pattern applied to the legged mobile robot, calculating means for calculating the moment generated on a ZMP as set by the second setting means by the leg motion, body trunk motion, upper limb motion and the altitude and height of the waist part as set, first finding means for finding an approximate solution of the waist motion, for which the moments as found by the calculating means are in equilibrium, using a non-precise model of the robot, second finding means for finding an approximate solution of the waist motion, for which the moments as found by the calculating means are in equilibrium, using a precise model of the robot, means for assuming a solution of the waist motion if a difference between the approximate solutions by the first and second finding means is less than a pre-set allowed value, means for correcting the moments of the non-precise model on the pre-set ZMP if the difference between the approximate solutions by the first and second finding means exceeds the pre-set allowed value and for re-throwing the corrected moments to the first finding means, and means for executing the full body exercise motion of the legged mobile robot based on the solution of the waist motion. The present invention also providers a corresponding control method.
In the operation control apparatus or method for the robot according to the second aspect, the non-precise model is a linear and/or non-interference multiple mass point approximating model for the robot. The precise model may be a rigid body model or a non-linear and/or interference multiple mass point approximating model for the robot.
In the operation control apparatus or method for the robot according to the second aspect, there may be provided a step or means for re-setting or correcting the pattern of the body trunk motion and upper limb motion, if the pre-set body trunk motion and upper limb motion cannot be realized with the approximate solution as found by the first finding means for finding the approximate solution of the waist motion by the non-precise model.
The first finding means for finding the approximate solution of the waist motion by the non-precise model may find the approximate solution of the waist motion by solving an equation of equilibrium between the leg motion, body trunk motion, upper limb motion and the moment on the pre-set ZMP produced by the external force pattern on one hand and the moment on the pre-set ZMP generated by motion within the horizontal plane of the waist part.
The first finding means for finding the approximate solution of the waist motion by the non-precise model may perform calculations on substituting a frequency-domain function for a time-domain function.
The first finding means for finding the approximate solution of the waist motion by the non-precise model may also find the approximate solution of the waist motion by applying Fourier expansion to moments on the pre-set ZMP generated by the leg motion, body trunk motion and the upper limb motion, by applying Fourier expansion to the moment on the pre-set ZMP produced by the external force pattern and to the motion in the horizontal plane of the waist part, by calculating Fourier coefficients of the trajectory of the horizontal plane of the waist part and by applying the inverse Fourier expansion.
The third setting means for setting the external force pattern predicts an external force pattern produced on applying an impact on an object at a pre-set speed based on the chronological external force process and a force application point when the external force pattern is applied to the object at a speed lower than the pre-set speed.
In a third aspect, the present invention provides a legged mobile robot including two or more movable legs, an upper body portion connected to the movable legs, means for detecting an external force applied from an external object to the movable leg and control means for adaptively controlling the motion of the movable leg and/or the upper body portion in accordance with detected results by the external force detecting means.
The legged mobile robot in the third aspect of the present invention is able to kick an external object, such as a ball, using e.g., one of the movable legs. The external force detection means detects the reactive force produced when the movable leg kicks the external object. The control means is able to adaptively control the operation of the movable leg and/or the upper body portion in accordance with the so-detected reactive force.
When the legged mobile robot kicks the external object, the mass and/or the repulsion coefficients of which is unknown, the movable leg kicks the external object at a speed lower than the pre-set speed for trial sake. In such case, the control means is able to predict the mass and/or repulsion coefficients when the robot kicks the object at the pre-set speed, based on an output of the external force detection means, by way of learning. When the robot actually kicks the external object at the pre-set speed, the operation of the movable leg and/or the upper body portion can be adaptively controlled in accordance with the results of the predictive learning.
With the legged mobile robot 100 according to the present invention, the robot kicking an external object of a pre-set mass may be prevented from being fallen down under an external force such as a reactive force applied from the kicked ball.
The legged mobile robot is able to continue the operation, as its attitude stability is kept, not only in the sole operation of kicking, but in a variety of operations of producing a certain motion of the object by exploiting a portion of the robot body or trunk.
Moreover, if, in the kicking operation, the mass or the repulsion coefficient of the kicked object, such as a soccer ball, is unknown, the operation of kicking the ball several times at a low speed not affecting attitude stability may be carried out several times at the outset to predict the reactive force applied to the robot on kicking at a high speed. As a result, attitude stability may be maintained when the robot kicks the object at an arbitrary speed.
The legged mobile robot embodying the present invention is able to take part as a player in a ball game exemplified by a soccer game or other athletic games in which the players perform their rolls in accordance with the game rule as an external force is applied to the players.
According to the present invention, as described above, there is provided a control mechanism for a legged mobile robot which may be extensively utilized in a human living space or environment.
According to the present invention, there may also be provided a control method mechanism in which the robot is able to continue the operation without falling as the attitude is adaptively controlled against variable external forces.
If, in the legged mobile robot of the present invention, the operation of kicking an object having a pre-set mass, the robot may be prevented from being fallen down under an external force such as a reactive force applied from the kicked ball.
It is also possible to continue the operation of the legged mobile robot, as its attitude stability is maintained, not only in the sole operation of kicking, but also in a variety of other operations exerting a pre-set motion on an object under exploitation of a portion of its body, such as hand, head or trunk.
It is moreover possible to predict the reactive force produced on actual kicking, by carrying out the operation of kicking an object at a low speed not affecting the attitude stability several times at the outset, even if the mass or the repulsion coefficient of the object is not known.
The legged mobile robot of the present invention is able to take part as a player in a ball game exemplified by a soccer game or other athletic games in which the players perform their rolls under application of an external force in accordance with the prescribed game rule.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention and the claims.